A substantial market has long existed for preassembled stretch frames for artwork and the like, for professional and amateur use. Stretch frames are rectangular in configuration and are formed of stretcher bars having generally standardized end structures for the meshing together of end portions in miter joints, these end portions including mitered outer sections, a tongue section and a tongue-receiving slot.
Prior art manufacturing and fabrication techniques for assembling stretcher bars into stretch frames, have been relatively inefficient and/or have required the utilization of expensive equipment or machinery. Such prior art assembly methods and techniques have been characterized by inefficient, relatively slow manual preassembly steps or operations, which substantially increase the cost in time and labor and limit output.
The assembly of conventional stretcher bars can required expensive apparatus for assembly, including such equipment as electronic sensors, electronic components, automatically operated stapling guns, etc.
In the interengaging of the end portions of mating stretcher bars, the extending tongues interfere with the tongue sections and mitered sections of mating bar end portions which define the slots of the mating bar end portions. Manual manipulation and trial-and-error are usually necessary to accomplish entry of tongue portions into slots of mating bars, and this is the first stage of assembly which must be accomplished. Once such entry is started, the end portions of mating bars can readily be urged together to define miter joints without difficulty, either manually or mechanically utilizing actuation means and appropriate fixtures. Unless initial entry of the tongue sections into the mating slots is effected, urging of the stretcher bar end portions together, as by mechanical means, results in damaging and crushing the bar end portions, so that many stretcher bars are scrapped.
It is therefore an object of the invention to provide stretcher bars having end portions with tongues adapted for rapid and proper entry into slots of mating stretcher bar end portions.
An object of the invention is to eliminate manual manipulation and trial-and-error in entry of stretcher bar tongue portions into slots of mating stretcher bars in the assembly of stretcher bars into stretch frames.
An object of the invention is to reduce the time, labor and costs of assembling stretcher bars into stretch frames.
An object of the invention is to provide apparatus for automatic assembly of stretcher bars into stretch frames with effective and rapid entry of stretcher bar tongue portions into slots of mating stretcher bars.
An object of the invention is to provide apparatus whereby entry of stretcher bar tongue portions into slots of mating bars is quickly and automatically effected.
An object of the invention is the provision of apparatus which eliminates the time and labor involved in manual preassembly of stretcher bar end portions in the assembly of stretch frames.
It is an object of the invention to enable the utilization of apparatus for assembling stretcher bars into stretch frames which is much less expensive than equipment otherwise required.